Fiber optic light conduits have been used for many years to transport light from one point to another through many different light transmitting media such as glass, plastic, and liquid using the principle of Total Internal Reflection (TIR). In each of these cases, some light is lost while traveling along the length of the light conduit for various reasons such as, but not limited to, absorption, light rays that exceed the critical angle of the optic, and diffusion due to optical imperfections such as bubbles, voids and debris.
It has been the goal of fiber optic manufacturers to minimize the amount of light loss along the optical conduit to maximize the light coming out of the output end thereby creating a more efficient optical fiber for end lighting purposes.
In recent years, there has been an interest in having a fiber optic that is efficient in maximizing the light output along the longitudinal axis to create a "glowing rod" effect that emulates a cathode tube, such as a fluorescent light. One problem has been that fiber optic conduits have not been able to create the intensity needed to be used in functional lighting applications as opposed to decorative type lighting.
Standard cathode lighting used for functional purposes generally requires some type of holder and/or reflector or lens to achieve the desired effect. One such example is in illuminating refrigerator interiors where the primary light target is at the front of the shelves. The cathode lamp output is very diffused and the refrigerator manufacturers presently use higher wattage lamps and special holder and/or reflectors to direct the amount of light required on the desired target area. However, higher wattage lamps result in higher heat output which is undesirable, because the refrigerator cooling elements may expend additional energy in order to compensate for the added heat.
Edge lighting with etched glass is another type of lighting which can be achieved with cathode tubes. However, one problem with this type related to efficiently directing the light into the edge of the glass, where the surface is typically 1/4 inch to 1/2 inch wide. This small area limits the ability of the cathode tube, even aided by a holder and/or reflector, to direct the light into the glass because the cathode tube is often the same width of the glass or larger, hence preventing a holder and/or reflector from focusing the light from the back side of the tube into the glass. Higher wattage lamps are required to achieve the desired illumination of the glass wasting even more light which is directed off away from the glass edge.
Many other problems exist with conventional linear functional and decorative lighting systems. Lamps are typically easily broken and eventually need to be replaced, thus the lamps must be installed in a protected chamber that must also provide access for lamp changing thereby creating construction and maintenance problems. Lamps typically cannot be bent or shaped easily and contain electrical components that can produce problems such as electrical shock or fire hazards, hence more complicated system designs are required to accommodate conventional lighting systems.
Many attempts have been made over the last several years to create a directional fiber optic light conduit that would provide a commercially acceptable side lighting as a light source to replace conventional linear lighting, such as cathode lighting. In U.S. Pat. No. 5,432,876, Appledorn discloses the creation of various cuts and notches that can be used to achieve back lighting as an alternative to conventional fluorescent light fixtures, but not as an alternative for direct lighting. One problem has been obtaining adequate brightness and directionality to achieve useful end product for direct lighting purposes.
An example of a directional fiber optic light conduit, commercially available from Lumenyte International Corporation in Costa Mesa, Calif., as "Clear Coat Optical Fiber", is disclosed in U.S. Pat. No. 5,067,831, issued to Robbins. When this product is used with a reflective "U" channel holder and/or reflector, the optical fiber conduit emits light out of its longitudinal sides, but the amount of light available, while fit for its intended purpose, is not enough to be useful for functional lighting applications.
Another example is disclosed in U.S. Pat. No. 4,422,719 issued to Orcutt. Orcutt describes an optical distribution system comprising essentially a fiber optic with cuts or bubbles made in the core and cladding, causing the light traveling down the optic to be interrupted and directed "outwardly." Although this is an improvement over an optical fiber conduit that has no cuts, the invention, as described, does not appear to create sufficient lighting for functional applications. Additionally, the product, as disclosed appears to be susceptible to damage by water and dust because the cuts are open to the environment in which the product is placed.
In U.S. Pat. No. 4,067,831, Robbins discloses the method of coating the optical fiber in a protective clear jacket that protects the optic fiber from damage, but when the light is projected outwardly from the cuts, a holder and/or reflector, on the opposite side of the jacket, has little effect on the overall intensity of light being projected outwardly from the cuts. While this product is fit for decorative lighting it fails to efficiently deliver sufficient light needed for functional lighting applications.
Another problem has been adequate resistance to fire. While the optical fiber does not prevent the dangers of electrical shock or fire hazard caused by conventional lighting systems, conventional fiber optic light conduit is manufactured using combustible materials. It is therefore desirable to have a fiber optic light conduit that is resistant to fire.